Autocatalytic copper plating process and solution



AUTOCATALYTIC COPPER 'PLATING PROCESS SOLUTION Allen E. 'Cahill and Vincent P. McConnell, Syracuse,

N. Y., assignors to General Electric Company, a corporation of New York 1 No Drawing. Application September 17, 1950' Serial No. 610,401

48 Claims. (Cl; 117130) The present invention relates to a copper plating process and solution.

More particularly, the invention relates to 'an autocatalytic chemical reduction process and bath for continuously plating desired thicknesses of copper on objects having catalytic metallic surfaces.

Heretofore, it has been necessary to electroplate copper onto the surfaces of objects where it is desired to have a relatively thick coating of copper (for'example up to five thousandths of an inch thick). While this method of copper plating is satisfactory for many purposes, it is objectionable in that it requires the use of rather elaborate and somewhatexpensive electrical equipment. Further, because of ditliculty in positioning the electrodes used in electroplating processes, it is often difiicult, if not impossible, "to electroplate irregularlyshaped objects.

There are some known techniques for obtaining flash coatings of chemical plated copper; however, these techniques utilize chemical solutions which decompose spontaneously during the plating process. In order to obtain any substantial thickness of chemically plated copper by these known techniques, it would require a number of such flash coatings. However, because the cheimcals in the solutions used in these techniques are spent in obtaining each such flash coating, such a procedure would be wasteful of chemicals, and hence too costly.

It is therefore one object of the present invention to provide new and improved commercially practicable copper plating solution and processes for the autocatalytic chemical plating of copper. I

Another object of the invention is to provide new and improved copper plating solutions andprocesses which are capable of plating any desired thickness of copper, up to a predetermined minimum thickness, onto objects having any desired surface configuration or shape.

A still further object of the invention is to provide new and improved chemical copper plating solutions which are relatively stable, and which do not decompose spontaneously during the plating action.

A still further object of the invention is to provide copper plating solutions and processes having the above listed characteristics whichdo not require elaborate electrical or other equipment for use in conjunction there with.

In practicing the invention an autocatalytic' chemical reduction process for continuously plating copper on objects having a catalytic metallic surface is provided: This process utilizes an aqueous solutionof a complex copper ion, a carbonate radical, a'hydroxid'e'radical, formaldehyde, and a complexing agent such as a tartrate or salicylate radical. For best results, the complex copper ion is present in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, and the. ratio between the complex copper ions 'and the carbonate ions in the bath expressed in moles per liter of solution is 'ice Patented Feb. 17, 1959 within the range of .20 to .60. In carrying out the process, the object to be plated is immersed in a solution comprised as stated above, and copper plating by auto'catalytic reaction of the solution at the catalytic metallic surface of the object takes place. During the plating action, the plating solution is circulated from a reservoir to a plating bath, and then back to the reservoir, The solution is heated to a temperature between and 100 centigrade before introduction into the plating bath, and is cooled to a temperature between 20 and 30 centigrade before returning the solution to the reservoir. If desired, the solution may be filtered prior to being returned to the reservoir; however, the composi tion of the plating solution must be maintained by adding to the portion of the solution contained in the reser- 5 voir, appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

It has long been known in the copper mirroring industry that'copper in alkaline solution can be reduced by formaldehyde. This familiar reaction is set forth in the following equation.

where the term (OH) represents a hydroxide radical, the term HCHO represents formaldehyde, the term Cu(II) represents a copper complex having the form the term HCOO- .is a formate radical, H O is water, and Cu the deposited copper. A copper plating solution that utilizes this reaction to achieve chemical copper plating isdisclosed in an article entitled Formation of Copper Films on Non-Conductorsa survey by Samuel Wein appearing in the Metal Finishing Magazine, August 1948 issue on page 58. The solution disclosed in the above-identified article, and all other previously known chemical copper plating solutions, achieve a flash coating of copper with a simultaneous breakdown or general decomposition of the chemicals of the solution. While the extremely thin films of copper obtained by these known flash coating solutions and techniques may be satisfactory for copper mirroring purposes, the thin films of copper thus obtained are not adequate for use (for example) to form electrical conductors capable of carrying considerable amounts of electric current. In order to obtain'sufiiciently thick copper films for such a purpose with previously known techniques, it would be necessary to carry out a number of flash coatings of the object to be copper plated. Because the chemicals in these copper plating solutions are decomposed during the flash coating process, the solutions are spent and cannot be regenerated. Hence, such a method of building up comparatively thick coatings of copper would be quite expensive, and prohibits the use of such procedure on a commercial scale.

The present invention is designed to achieve copper plating by the reduction of Cu(II) in a system in [F. Hartwagner, Z. Anal. Chem. 52, 17-20, 1913], which the reaction represented by Equation 2 is taking place. The above'Reaction 2' is catalyzed by a copper surface. Cu(II) is reduced by the H produced or by the activated complex in Reaction 2. The plating, therefore, is an autocatalytic process. That is, the plated copper surface itself serves as a catalyst to the reaction leading to copper plating. Hence, any desired thickness of copper plating may be built up on the object to be plated. This autocatalytic chemical copper plating action is achieved by stabilizing the plating solution used in In accordance with the a part of the present invention. It is this copper complex that takes part in the'reaction set forth in Equation 3 to efiect autocatalytic copper plating on objects having a catalytic metallic surface.

a desired temperature range for the particular ingredients 5 The following lists of copper salts, among others, are used to make up a particular plating solution, and the use suitable for forming the copper complex identified in the of a suitable stabilizing agent in proper amounts. When reaction of Equation 4. These copper salts are cupric thus properly constituted, the plating solution does not desalicylate, cupric tartrate, cupric carbonate, cupric nitrate, compose generally, and will autocatalytically plate copper cupric chloride, cupric sulfate, and cupric hydroxide. A on certain catalytic metallic surfaces. Further, because typical reaction involving one of these copper salts and this plating reaction takes place without any general detartaric acid to form the desired copper complex is set composition of the plating solution, the plating process forth in Equation 5,'and is exemplary of the complexing can be continued over long periods of time by continuous action of the tartrate radical on any of the copper salts regeneration of the chemicals of the bath that are spent by identified above.

reason Of the plating aCtlOI'l.

COMPOSITION OF PLATING SOLUTION COOlSCu[COOCI-IOCHO In any copper plating process attempting to carry out COO] -+4H++2NO3 the reactions set forth in Equations 2 and 3, it is of course Byv comparison of Equation 5 to Equation 4, it can be essential that a plating solution be provided wherein all appreciated that the reactions set forth therein are identiof the constituents listed in Equations 2 and 3 are present. cal except for the fact that Equation 4 expresses the re- In order to provide a chemical copper plating bath having action in general terms. the proper constituents, and the proper proportions of The tartrate radical required in the reaction set forth such constituents, and thereby obtain the stable characterin Equation 4, may be supplied from any one of the folistics required for autocatalytic chemical copper plating lowing lists of tartrate bearing compounds, amongst in accordance with the invention, it is necessary that the others. These compounds aretartaric acid, sodium tar-- constituents of the plating bath fall within the proportions trate, potassium tartrate, cupric tartrate and sodium polisted in the below-set-forth Table No. 1. Table No. l tassium tartrate. identifies three general types of plating solutions formed In addition to the tartrate radical, it has been disin accordance with the present invention, and identifies the covered that the salicylate radical will serve as a suitable constituents of the solutions. The constituents of the socomplexing agent for carrying out a complexing reaction lutions are listed in moles per liter of solution, and the similar to that set forth in Equation 4. No formulation solutions set forth are intended to be operated within the of the salicylate complexing reaction has been worked temperature range of 20 degrees to 100 degrees centigrade. out at this time; however, it has been observed that Table No. 1

Plating solution type I II III Limits of proportions in moles per liter of solution Low High Low High Low High Complex copper ion, [Ou(l'l)] 0.06 0. 12 0.06 0.12 0.06 0.12 Hydroxide radical, (0H) 0.5 1.5 0.5 1.5 0.5 1.5 Formaldehyde, (HOH 0.3 5.0 0.3 5.0 0.3 5.0 Carbonate, (003') 0.06 0.5 0.06 0.5 0.06 0.5 Tartrate, [COO-OH(OH)-GH(OH)COO]- 0.1 0.4 0.1 0.4 salicylate, (HOCaHiCOO') 0. 1 0. 4 0.01 :0. 4

Water, (H20) Remaiuderto 1 liter In addition to the above conditions, for the best results, it is desirable that the ratio between the complex copper ions and the carbonate ions in the plating solution expressed in moles per liter of solution be within the range .20 to .60.

One of the difiiculties encountered in providing a chemical copper plating solution is the tendency of the copper ions to go out of solution. To overcome this difiiculty, it has proven necessary to complex the copper ions by means of a suitable complexing agent added to the plating solution. One known suitable complexing agent is described in the Journal of the Indian Chemical Society, volume 27, No. 12, 1950, in a series of articles entitled Metallic Complexes of Tartaric and Citric Acids; Part I, Copper-Tartaric Acid, pages 443-454; and Part II, Copper-Akali Tartrate, pages 683 to 690, by R. N. Sen Sarma. This complexing agent reacts with the copper ions in the following general manner to form a copper complex that is readily maintained in solution.

It can be appreciated from an examination of Equation salicylate will hold the copper ions in solution in a fashion similar to tartrate, and for this reason it is believed that salicylate complexes the copper ion in a similar manner.

Suitable ingredients for providing a salicylate radical to a plating solution in order to achieve this end are set forth in the following list. These ingredients aresalicyclic acid, sodium salicylate, potassium salicylate and cupric salicylate.

In' addition to both the tartrate and salicylate radicals, ithas been determined that combinations of tartrate and salicylate in a plating bath can achieve complexing of the copper ion in the manner set forth in the reaction of Equation 4. Any of the particular tartrate or salicylate bearing ingredients set forth in the above lists are suitable for-use in combination to achieve the desired complexing. From theresults obtained by using salicylate alone, and combinations of salicylatewith tartrate, as a complexing agent, it appears that the tartrate radical performs somewhat better as a complexing agent. This belief is based on the fact that less filtering of plating solutions using tartrate was required after extended periods of use of. the plating solutions; hence indicating, that if the tartrate is used as a complexing agent, or if it is present with. salicylate, there is a little less decom- P on of the plating solution after extended eriods of use.

In addition to the presence of a copper complex, the reaction set forth in Equations 2 and 3 requires the presence of a formaldehyde radicalwhich serves as a reducing agent. This formaldehyde radical may be supplied from a pure or aqueous solution of formaldehyde.

To complete the reaction set forth in Equation 2, it is necessary to provide a hydroxide radical which is believed to catalyze the reaction. Amongst others, suitable sources of the hydroxide radical aresodium hydroxide, potassium hydroxide and cupric hydroxide.

In order that the copper plating reaction set forthvin Equations 2 and 3 take place autocata'lytically, it is essential that no general spontaneous decomposition of the bath or plating solution take place. To prevent any such spontaneous general decomposition of the plating solution, it was determined that a stabilizing agent was required in the solutions in order to assure autocatalytic reduction of copper at the surface of objects having catalytic metallic surfaces immersed in the solutions. Further, it was discovered that the carbonate radical provided the most eifective stabilizing agent for plating solutions of this character, and that the ratio of the complex copper ions present in the solution to the carbonate ions, was fairly critical. For best results, this ratio expressed The plating baths listed in Table No. 2 were made up of the following ingredients expressed in'grams/liter unless otherwise indicated.

Salicylic acid (HOC H COOH) 80 gms./l. Water (H O), remainder to one liter.

. Bath #3:

1n moles per liter of solution should range between .2

and .6. In addition to stabilizing the plating solution, g g i g 6% fi' it is believed that the carbonate radical also serves to g 5 i g 5 67 help keep the copper ions in solution; hence, the car- Orma e y e 0 3 bonate radical serves as a complexing agent in a manner Sodium bicarbonat (NaHCO 5 so y somewhat similar to tartrate and salicylate. Amongst S 3 others, suitable sources of carbonate for use as a stabiliz- 0 mm Potasslum tartrate ing agent aresodium carbonate sodium bicarbonate, (.NaKc4H4O6'4H2O) 75 gms'/ i Sal1cyl1c acid (HOC H COOH) 50 gms./l. potassium carbonate, potassium bicarbonate, cupric car- W H O d bonate, and basic cupric carbonate. ater 2 remam er to one The manner in which the new and improved chemical Bath #4: copper plating solutions are made up, can be quite im- Cupric chloride (CuCl .2H O) l2 gms./l. portant in that if the ingredients are placed in the plat- Sodium hydroxide (NaOH) 35 gms./l. ing solution in an improper order, it may vary well Formaldehyde (HCHO) 50 ml., 36% happen that not all the ingredients will become dissolved solution. in the solution. For this reason, the following pro- 40 Sodium bicarbonate (NaHCO;,)... 5 gms./l. cedure is suggested for making up copper plating solu- Salicylic acid (HOC H COOH) gms./l. tions in accordance with the invention. First dissolve Water (H O), remainder to one liter. the copper containing salt in a quantity of water to form Bath a first solution. Next dissolve the tartrate and/or salicylate salts in a quantity of water to form a second g chlonde. (cuclzzHao) 20 T odium hydroxlde (NaOH) 20 gms./l. solution. Then dissolve the hydroxide and carbonate Formaldeh d (HCHO) 30 1 bearing ingredients in a quantity of water to form a y e fi third solution. Add the first and second solutions to.- t gether, and to the resulting mixture add the third solu- Sodium bwarbonat? (NaHCOa)"" 25 gms'/ 50 Sodium potassium tartrate tion. Finally, add formaldehyde and a quantity of Water (NaKC H 0 4H 0) 80 S A necessary to bring the total to one liter to make up the Water 2 T; gm plating solution. It is, of course, understood that the 2 rem 1 er 0 one 1 quantities of ingredients added are in accordance with h #6 teachings of the above tables, and that the solutions are Cupric sulfate (CuSO4)---.- 30 gms./l. maintained within the temperature range prescribed. Sodium hydroxide (NaOH) 50 gms./l. Examples of six different plating solutions made upin Formaldehyde (HCHO) 200 ml., 36% accordance with the teachings of the invention, are set solution. forth in Table No. 2 below, and brief descriptions of the Sodium bicarbonate (NaHCO 25 gms./l. particular ingredients used in forming each solution are Sodium potassium tartrate listed. Concentrations in Table No. 2 are given in moles/ 4H4 2O) v80 gms./l. liter. W t r (H O), remainder to one liter.

Table No. 2

Temperature rangeindegrees eentigrade 20-30 4052 75 80100 2530 Plating Solution -#1 4 #2 #8 #4 #5 #6 Copper complex [Ou(II)] a 0.062 0.117 0.07 0.07 0.117 0.12 Hydroxide 0.5 1.25 0.875 0.875 .05 1.25 Formaldehyde 1.1 I .88 .55 .55 .33 .22 Carbonate v 0.12 .476 .00 .06 .30 .30 Tartrate 016 227 266 283 .283 Salicylate .58 v .362 .362

Solvent (H O) i I Remainder of solution up to lliter -7 AUTOCATALYTIC COPPER PLATING PROCESS The present invention further comprises an autocatalytic chemical reduction process for plating catalytic metallic surfaces with copper. This process has been found to provide selective chemical deposition of copper on catalytic metallic surfaces with no appreciable copper beingprecipitated to the bottom of the reaction vessel containing the plating solution, or being deposited on its walls. The copper is deposited in substantially pure, metallic form, and has good adhesion to the catalytic metallic surface being plated. In tests, the autocatalytically chemically plated copper has been found to have substantially the same properties as electrodeposited copper plating.

In carrying out the process, the source of plating copper is a complex copper ion contained in the plating solution, and upon an object to be plated being immersed in the plating bath, the reaction set forth in Equation 2 is catalyzed by the catalytic metallic surface of the object. Metals which serve to catalyze the reaction set forth in Equation 2 include copper, and as copper is produced by Reaction 3, it can be stated that the reaction is autocatalytic, and that copper can be plated to any desired thickness within certain practical limits. Other metals which are known to catalyze the reaction set forth in Equation 2 are nickel, silver, palladium,platinum, and gold. It is, of course, possible to provide an object with a catalytic metallic surface in order to copper plate the same by means of the present invention. For example, nickel is known to be a catalytic material and all of the following list of elements can be nickel-plated by means of the autocatalytic chemical reduction of nickel in the presence of a low concentration of hypophosphite as taught by Brenner and Ridell in an article entitled Nickel Plating on Steel by Chemical Reduction, Journal of Research of the National Bureau of Standards, volume 37, July 1946, pages 31 to 34. These materials are copper, silver, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium, and platinum. Additionally, by proper treatment of the surface thereof in a known manner, it is possible to provide a sheet of insulating material,such as a phenolic plastic, with a catalytic metallic surface. This may be achieved, for example, by providing the sheet of insulating material with a flash coating of silver or nickel or other metallic crystals on the areas desired to be copper plated, and subsequently immersing the catalyzed sheet of material in a bath prepared in accordance with the present invention. In this manner, it is possible to autocatalytically deposit a layer of copper on the sheet of insulating material which is sufiiciently thick to serve as an electrical conductor, for example.

Having provided the object to be copper plated with a catalytic metallic surface, if the object is not formed from a catalytic metallic material, the object is then ready to be plated by immersing the same in a plating solution prepared in accordance with the teachings set forth above. No special prel-plating treatment of the object is required other than providing it with a catalytic metallic surface, and seeing that the catalytic metallic surface is clean. Any of the conventional methods of cleaning metallic surfaces may be used insofar as cleaning of the catalytic metallic surface is concerned. For example, water rinsing has been proven to be quite adequate in many instances. The object to be plated is then immersed in the plating bath in a manner such that all of the surface to be plated is exposed to the plating solution. It has been determined, that the size of the object or surface to be plated with respect to the size of the reaction vessel in which the plating solution is contained, is not too critical. As is to be expected, however, the larger the object to be plated with respect to the total amount of plating solution available, the faster the ingredients of the plating solution willbe used'in the plating reaction, and the faster such ingredients must be replenished. For this reason, there is an optimum relationship to be maintained between these two parameters in order that the proportions-of the constituents of the solutions be maintained within the range of values listed in Table No. 1. It is of course essential that the objects being plated be immersed in the plating solution for a sufficiently long period of time to build up the thickness of the plated copper to a desired value. 1

Upon immersion of the object to be plated in the copper plating solution, the immersed object is copper plated by autocatalytic reaction of the solution at the catalytic metallic surface of the object. This reaction is depicted by Equations 2 and 3 and results in the deposition of copper on the catalytic metallic surface of the object. In carrying out. the copper plating reaction depicted by Equations 2 and 3 the copper salts, the hydroxide radical and the formaldehyde radical become depleted, consequently, it is necessary to continually replenish the supply of these constituents during the plating action. Accordingly, if the plating reaction is to be carried out on a commercial scale wherein large numbers of objects are plated over extended periods of time, it is desirable that a suitable installation for continuous regeneration of the plating solution be provided. For this reason, any installation that is designed to carry on extended plating operations by means of the present invention, should include both a reservoir for the plating solution, and a reaction vessel or plating bath in which plating takes place, together with equipment for circulating the plating solution between the reservoir and the plating bath. Additionally, means must be provided for heating the plating solution to a temperature between 20 degrees and degrees centigrade before introduction into the plating bath, and means should be provided for cooling the plating solution to a temperature between 20 degrees and 30 degrees centigrade before returning the solution to the reservoir. It is also desirable that'the plating solution be filtered at some stage subsequent to cooling of the solution, and prior to its being reheated. Further, in order to revitalize the constituents of plating solution that are depleted during the plating action, the portion of the plating solution contained in the reservoir should have appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents added thereto. In this manner the proportions of the constituents of the plating solution are maintained so that they always fall within'the prescribed range of values set forth in Table No. l f

By means of the present invention, it has been possible to build up chemically deposited copper coatings having a total thickness as great as .004 inch, at a rate of about .00008 inch per hour. The resulting copper coatings were determined to have good mechanical adhesion to the objects upon which they were plated, and to provide a coating comparable to electrodeposited copper.

From the foregoing description, it can be appreciated that the invention provides 'a commercially practicable chemical copper plating solution and process for the autocatalytic chemical plating of copper on objects having catalytic metallic surfaces. By means of the invention relatively thick coatings of copper may be plated without requiring the use of elaborate and expensive electrical equipment, and yet, any desired thicknesses of copper plating may be formed up to predetermined maximum thickness limits. Further, chemical copper plating may be readily formed on irregularly shaped objects and surfaces, and assures that such' irregularly shaped objects and surfaces will receive a uniform coating of copper. Also the invention provides a plating solution and process capable of carrying out the above objectives which is relatively stable, and easy to operate. This characteristic allows those portions of the plating solution which are exhausted during continuous and extended plating operations to be continuously renewed by supplying to the plating solution appropriate amounts of the depleted reagents, thereby making feasible chemical copper plating operations on a commercial scale.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical, formaldehyde and a complexing agent.

2. The bath set forth in claim 1 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

3. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical, formaldehyde, and a complexing agent comprising a tartrate radical.

4. The bath ,set forth in claim 3 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the ratio between the com plex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60 and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

5. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface essentially comprising an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical, formaldehyde, and a complexing agent comprising a salicylate radical, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution being within the range .20 to .60, and the temperature of the bath being maintained between 20 degrees and 100 degrees centigrade.

6. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface essentially comprising an element selected from the group consisting of nickel, silver, palladimn, copper, platinum and gold, the bath essentially comprising an aqueous solution of a complex copper ion [Cu(II)] present in an amount from .06 to .12 mole per liter of solution, a carbonate radical (CO present in an amount from .06 to .50 mole per liter of v solution, a hydroxide radical (OH*), formaldehyde (HCHO) a tartrate radical 10 in the bath expressed in moles per liter of solution being within the range .20 to .60, and the temperature of the bath being maintained between 20 degrees and degrees centigrade.

7. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complexcopper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, and formaldehyde present in an amount from 1.0 to 5.0 moles per liter of solution.

8. The bath set forth in claim 7 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum'and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degreescentigrade.

9. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface essentially comprising an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, and a tartrate radical, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution being within the range .20 to .60, and the temperature of the bath being maintained between 20 degrees and 100 degrees centigrade.

10. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface essentially comprising an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 moles per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, a tartrate radical, and a salicylate radical, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution being within the range .20 to .60, and the temperature of the bath being maintained between 20 degrees and 100 degrees centigrade.

11. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface essentially comprising an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the

bath essentially comprising an aqueous solution of acom plex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, and a salicylate radical, the ratio between the complex copper.

ions and the carbonate ions in the bath expressed in moles per liter of solution being within the range .20 to .60, and the temperature of the bath being maintained between 20 degrees and 100 degrees centigrade.

12. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution-of a complex copper ion present in an amount from 0.6 to .12 moles per liter of solution, a carbonate radical present in an amount from .06

to .50 mole per liter of solution, a hydroxideradical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, a tartrate radical present in an amount from .10 to .40 mole per liter of solution, and a salicylate radical present in amount from to .40 mole per liter of solution.

13. The bath set forth in claim 12 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

14. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, and a salicylate radical present in amount from .10 to .40 mole per liter of solution.

15. The bath set forth in claim 14 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

16. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion formed from a copper salt selected from the group consisting of cupric salicylate, cupric tartrate, cupric carbonate, cupric nitrate, cupric chloride, cupric sulfate, and cupric hydroxide, a carbonate radical selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cupric carbonate, basic cupric carbonate, formaldehyde selected from pure or an aqueous solution of formaldehyde, a hydroxide radical selected from the group consisting of sodium hydroxide, potassium hydroxide, and cupric hydroxide, and a complexing agent.

17. The bath set forth in claim 16 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution; the carbonate radical is present in the amount from .06 to .50 mole per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

18. The bath set forth in claim 14 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from 0.6 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.5 moles per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

12 19. A bath for the autocatalytic'chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion formed from a copper salt selected from the group consisting of cupric salicylate, cupric tartrate, cupric carbonate, cupric nitrate, cupric chloride, cupric sulfate, and

cupric hydroxide, a carbonate radical selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cupric carbonate, and basic cupric carbonate, a hydroxide radical selected from the group consisting of sodium hydroxide, potassium hydroxide and cupric hydroxide, formaldehyde from pure or an aqueous solution of formaldehyde, a tartrate radical selected from the group consisting of tartaric acid, sodium tartrate, potassium tartrate, cupric tartrate, and sodium-potassium tartrate, and a salicylate radical selected from the group consisting of salicylic acid, sodium salicylate, potassium salicylate, and cupric salicylate.

20. The bath set forth in claim 19 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, and the carbonate radical is present in the amount from .06 to .50 mole per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and degrees centrigrade.

21. The bath set forth in claim 19 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12. mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.5 moles per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

22. The bath set forth in claim 19 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, pal ladrum, copper, platinum and gold, the complex copper 10m 18 present in the solution in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present inan amount from .50 to 1.50 moles per liter of solution, the tartrate radical is present in an amount from .10 to .40 mole per liter of solution, and the salicylate radical is present in an amount from 0 to .40 mole per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath is within the range of .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

23. A bath for the autocatalytiif chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion formed from a copper salt selected from the group consisting of cupric salicylate, cupric tartrate, cupric carbonate, cupric nitrate, cupric chloride, cupric sulfate, and cupric hydroxide, a carbonate radical selected from the group consisting of sodium carbonate, sodium I bicarbonate, potassium carbonate, potassium bicarbonate, cupric carbonate and basic cupric carbonate, a hydroxide radical selected from the group consisting of sodium hydroxide, potassium hydroxide, and cupric hydroxide, formaldehyde selected from pure or an aqueous solution of formaldehyde, and a tartrate radical selected from the group consisting of tartaric acid, sodium tartrate, potassium tartrate, cupric tartrate, and sodium-potassium tartrate.

24. The bath set forth in claim 23 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, and the carbonate radical is present in the amount from .06 to .50 mole per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

25. The bath set forth in claim 23 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.5 moles per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

26. A bath for the autocatalytic chemical plating of copper on a catalytic metallic surface, the bath essentially comprising an aqueous solution of a complex copper ion formed from a copper salt selected from the group consisting of cupric salicylate, cupric tartrate, cupric carbonate, cupric nitrate, cupric chloride, cupric sulfate, and cupric hydroxide, a carbonate radical selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cupric carbonate,'and basic cupric carbonate, a hydroxide radical selected from the group consisting of sodium hydroxide, potassium hydroxide, and cupric hydroxide, formaldehyde selected from pure or an aqueous solution of formaldehyde, and a salicylate radical selected from the group consisting of salicylic acid, sodium salicylate potassium salicylate, and cupric salicylate.

27. The bath set forth in claim 26 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, and the carbonate radical is present in the amount from .06 to .50 mole per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath i maintained between 20 degrees and 100 degrees centigrade.

28. The bath set forth in claim 26 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.5 moles per liter of solution, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, and the temperature of the bath '14 is maintained between 20 degrees and degrees centigrade.

29. The bath set forth in claim 26 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5 .0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.50 moles per liter of solution, the salicylate radical is present in an amount from .10 to .40 mole per liter of solution, the ratio between the complex copper ion and the carbonate ions in the bath is within the range .20 to .60, and the temperature of the bath is maintained between 20 degrees and 100 degrees centigrade.

30. An autocatalytic chemical reduction process for continuously plating copper on objects having a catalytic metallic surface comprising the steps of providing an aqueous solution of a complex copper ion, a carbonate radical, a hydroxide radical, formaldehyde, and a complexing agent, immersing an object to be plated in said solution, and copper plating said immersed object by autocatalytic reaction of said solution at the catalytic metallic surface of the object.

31. The process set forth in claim 30 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the temperature of the aqueous solution is maintained between 20 degrees and 100 degrees centigrade, and the solution is continuously regenerated during plating by adding thereto appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

32. An autocatalytic chemical reduction process for continuously plating copper on objects having a catalytic metallic surface comprising the steps of providing an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical, formaldehyde, and a complexing agent, immersing an object to be plated in said solution, and copper plating the immersed metal object by autocatalytic reaction of said solution at the catalytic metallic surface of the object.

33. The process set forth in claim 32 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, the temperature of the aqueous solution is maintained between 20 degrees and 100 degrees centigrade, and the solution is continuously regenerated during plating by adding thereto appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

34. An autocatalytic chemical reduction process for continuously plating copper on objects have a catalytic metallic surface comprising the steps of providing an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, and formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, and a complexing agent, immersing an object to be plated in said solution, and copper plating the immersed object by autocatalytic reaction of said solution at the catalytic metallic surface of the object.

35. The process set forth in claim 34 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, the temperature of the aqueous solution is maintained between 20 degrees and 100 degrees centigrade, and the solution is continuously regenerated during plating by adding thereto appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

36. An autocatalytic chemical reduction process for continuously plating copper on objects having a catalytic metallic surface comprising the steps of providing an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, a tartrate radical present in an amount from -.10 to .40 mole per liter of solution, and a salicylate radical present in an amount from to .40 mole per liter of solution, immersing an object to be plated in said solution, and copper plating the immersed object by autocatalytic reaction of said solution at the catalytic metallic surface of the object.

37. The process set forth in claim 36 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range of .20 to .60, the temperature of the aqueous solution is maintained between 20 degrees and 100 degrees centigrade, and the solution is continuously regenerated during plating by adding thereto appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

38. An autocatalytic chemical reduction process for continuously plating copper on objects having a catalytic metallic surface comprising the steps of providing an aqueous solution of a complex copper ion present in an amount from .06 to .12 mole per liter of solution, a carbonate radical present in an amount from .06 to .50 mole per liter of solution, a hydroxide radical present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde present in an amount from .30 to 5.0 moles per liter of solution, and a salicylate radical present in an amount from .10 to .40 mole per liter ofsolution, immersing an object to be plated in said solution, and copper plating said immersed object by autocatalytic reaction of said solution at the metallic surface of the object.

39. The process set forth in claim 38 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60, the temperature of the aqueous solution is maintained between 20 degrees and 100 degrees centigrade, and the solution is continuously regenerated during plating by adding thereto appropriate amounts of soluble copper, hydroxide and formaldehyde containing reagents.

40. The continuous process of autocatalytically chemically plating objects having a catalytic metallic surface with copper which comprises providing a plating bath essentially comprising anaqueous solution of complex copper ions, a carbonate radical, a hydroxide radical, formaldehyde, and a complexing agent, circulating the solution from the reservoir to the plating bath and then back'to the reservoir, heating the solution to a temperature between 20 degrees centigrade to degrees Centigrade before introduction into the plating bath, cooling the solution to a temperature between 20 degrees Centigrade and 30 degrees centigrade before returing the solution to the reservoir, immersing the object to be plated in the plating bath for a time interval corresponding to the thickness of the copper plating desired, copper plating said object by autocatalytic reaction of the solution at the catalytic metallic surface of the object, and maintaining the composition of the plating solution by adding to the portion thereof contained in the reservoir appropriate amounts of soluble copper, hydroxide, and formaldehyde containing reagents.

41. The continuous process of autocatalytically chem ically plating objects having a catalytic metallic surface with copper which comprises providing a plating bath essentially comprising an aqueous solution of complex copper ions, a carbonate radical, a hydroxide radical, formaldehyde, and a complexing agent, circulating the solution from a reservoir to the plating bath and then back to the reservoir, heating the solution to a temperature between 20 degrees to 100 degrees centigrade before introduction into the plating bath, cooling the solution to a temperature between 20 degrees and 30 degrees centigrade before returning the solution to the reservoir, filtering the solution subsequent to cooling and prior to reheating the same, immersing the object to be plated in the plating bath for a time interval corresponding to the thickness of the copper plating desired, copper plating the object by autocatalytic reaction of the solution at the catalytic metallic surface of the object, and maintaining the composition of the plating solution by adding to the portion thereof contained in the reservoir appropriate amounts of soluble copper, hydroxide, and formaldehyde containing reagents.

42. The process set forth in claim 41 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in the amount from .06 to .50 mole per liter of solution, and the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution being within the range .20 to .60.

43. The process set forth in claim 41 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladiurn, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical present in an amount from .50 to 1.5 moles per liter of solution, and the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60.

44. The continuous process of autocatalytically chemically plating objects having a catalytic metallic surface with copper which comprises providing a plating bath essentially comprising an aqueous solution of complex copper ions, a carbonate radical, a hydroxide radical, formaldehyde, and a tartrate radical, circulating the solution from a reservoir to the plating bath and then back to the reservoir, heating the solution to a temperature between 20 degrees to 100 degrees centigrade before introduction into the plating bath, cooling the solution to a temperature between 20 degrees and 30 degrees centigrade before returning the solution to the reservoir, filtering the solution subsequent to cooling and prior to reheating the same, immersing the object to be plated in the plating bath for a time interval corresponding to the thickness of the copper plating desired, copper plating the object by autocatalytic reaction of the solution at the catalytic metallic surface of the object, and maintaining the composition of the plating solution by adding to the portion thereof contained in the reservoir appropriate amounts of soluble copper, hydroxide, and formaldehyde containing reagents.

45. The continuous process of autocatalytically chemically plating objects having a catalytic metallic surface with copper which comprises providing an aqueous solution of complex copper ions, at carbonate radical, a hydroxide radical and formaldehyde, a tartrate radical, and a salicylate radical, circulating the solution from a reservoir to the plating bath and then back'to the reservoir, heating the solution to a temperature between 20 degrees to 100 degrees centigrade before introduction into the plating bath, cooling the solution to a temperature between 20 degrees and 30 degrees centigrade before returning the solution to the reservoir, filtering the solution subsequent to cooling and prior to reheating the same, immersing the object to be plated in the plating bath for a time interval corresponding to the thickness of the copper plating desired, copper plating the object by autocatalytic reaction of the solution at the catalytic metallic surface of the object, and maintaining the composition of the plating solution by adding to the portion thereof contained in the reservoir appropriate amounts of soluble copper, hydroxide, and formaldehyde containing reagents.

46. The process set forth in claim 45 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum, and gold, the complex copper ion is present in the solution in an amount from .06

to .12 mole per liter of solution, the carbonate radical is present in an amount from .06 to .50 mol per liter of solution, the hydroxide radical is present in an amount from .50 to 1.50 moles per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the tartrate radical is present in an amount from .10 to .40 mole per liter of solution, the salicylate radical is present in an amount from 0 to .40 mole per liter of solution, and the ratio between the complex copper ions and the carbonate ions in the bath expressed in moles per liter of solution is within the range .20 to .60.

47. The continuous process of autocatalytically chemically plating objects having a catalytic metallic surface with copper which comprises providing an aqueous solution of complex copper ions, a carbonate radical, a hydroxide radical, formaldehyde, and a salicylate radical circulating the solution from a reservoir to the plating bath and then back to the reservoir, heating the solution to a temperature between 20 degrees to degrees centigrade before introduction into the plating bath, cooling the solution to a temperature between 20 degrees and 30 degrees centigrade before subsequent to cooling and prior to reheating the same, immersing the object to be plated in the plating bath for a time interval corresponding to the thickness of the copper plating desired, copper plating the object by autocatalytic reaction of the solution at the catalytic metallic surface of the object, and maintaining the composition of the plating solution by adding to the portion thereof contained in the reservoir appropriate amounts of soluble copper, hydroxide, and formaldehyde containing reagents.

48. The process set forth in claim 47 wherein the catalytic metallic surface essentially comprises an element selected from the group consisting of nickel, silver, palladium, copper, platinum and gold, the complex copper ion is present in the solution in an amount from .06 to .12 mol per liter of solution, the carbonate radical is present in an amount from .06 to .50 mole per liter of solution, formaldehyde is present in an amount from .30 to 5.0 moles per liter of solution, the hydroxide radical is present in an amount from .50 to 1.50 moles per liter of solution, the salicylate radical is present in an amount from .10 to .40 mole per liter of solution, and the ratio between the complex copper ions and the carbonate radical in the bath is within the range .20 to .60.

References Cited in the file of this patent UNITED STATES PATENTS 1,607,676 Jirotka Nov. 23, 1926 2,278,722 Loiseleur Apr. 7, 1942 2,410,626 Boudreau Nov. 5, 1946 2,643,199 Hersch June 23, 1953 FOREIGN PATENTS 343,435 Italy Sept. 29, 1936 490,159 Great Britain Aug. 10, 1938 503,034 Great Britain Mar. 30, 1939 163,378 Australia June 17, 1955 OTHER REFERENCES The Glass Industry, Marboe et al., vol. 26, No. 3, pages 138 and 142, March 1945.

Handbook of Chemistry and Physics, published by the Chemical Rubber Company, 35th edition, 1953-1954 (page S 14 relied on). 

30. AN AUTOCATALYTIC CHEMICAL REDUCTION PROCESS FOR CONTINUOUSLY PLATING COPPER ON OBJECTS HAVING A CATALYTIC METALLIC SURFACE COMPRISING THE STEPS OF PROVIDING AN AQUEOUS SOLUTION OF A COMPLEX COPPER ION, A CARBONATE RADICAL, A HYDROXIDE RADICAL, FORMALDEHYDE, AND A COMPLEXING AGENT, IMMERSING AN OBJECT TO BE PLATED IN SAID SOLUTION, AND COPPER PLATING SAID IMMERSED OBJECT BY AUTOCATALYTIC REACTION OF SAID SOLUTION AT THE CATALYTIC METALLIC SURFACE OF THE OBJECT. 